The isolation and characterization of a peptide component of thymosin fraction 5 termed thymosin .alpha..sub.1, was described in U.S. Pat. No. 4,079,127. Thymosin .alpha..sub.1 contained 28 amino acid residues and was an acidic peptide having a pl of about 4.0-4.3. It is further distinguished in having a blocked amino terminal (N-acetyl). Biologically thymosin .alpha..sub.1 is active in the MIF, E-rosette and mitogen assays but is not active in the mixed lymphocyte response (MLR) assay. The amino acid sequence for thymosin .alpha..sub.1 is as follows:
(N-acetyl)-Ser-Asp-Ala-Ala-Val.sup.5 -Asp-Thr-Ser-Ser-Glu.sup.10 -lle-Thr-Thr-Lys-Asp.sup.15 Leu-Lys-Glu-Lys-Lys.sup.20 -Glu-Val-Val-Glu-Glu.sup.25 -Ala-Glu-Asn-OH
Goldstein et al., J. of Reticuloendothelial Society 23, 253 (1978) described partially purified thymosin .beta..sub.3 and .beta..sub.4 as components of thymosin fraction 5 and gross physical data is given. Additionally, Low and Goldstein in Year In Hematology 1978, Siber et al. ed. (Plenum Pub. Co. 1978) at p. 281 indicated that partially purified thymosin .beta..sub.3 and .beta..sub.4 induce TdT positive cells in T-cell populations.
The sequence for thymosin .beta..sub.3 and .beta..sub.4 advanced in the parent application, Ser. No. 967,675, has been revised in amino acids 24-35 by exchanging original sequence 30-35 for original sequence 24-29 of both peptides. This revision is based on additional data derived from thermolysin digests used in the peptide mapping.